Drop support for XEmacs package EFS

Drop support for XEmacs package EFS

EFS is a long defunct XEmacs-specific fork of Ange FTP that is
superseded by TRAMP.
* lisp/ffap.el (ffap-ftp-default-user)
(ffap-replace-file-component, ffap-host-to-filename):
* lisp/gnus/mml.el (mml-parse-file-name):
* lisp/gnus/nnheader.el (nnheader-re-read-dir):
* lisp/net/browse-url.el (browse-url-filename-alist):
* lisp/speedbar.el (speedbar-check-vc): Drop support for XEmacs
package EFS.